This invention relates generally to reducing thrombosis and more particularly to a method and apparatus for imposing an electronegative potential at a site where thrombosis is likely to be a problem to reduce platelet congregation.
It is common practice to repair the narrowed segment of a diseased blood vessel by radially expanding the affected area of the blood vessel using a balloon catheter, commonly called balloon angioplasty. Early failure of such vascular repairs can occur shortly after the application of balloon angioplasty (commonly within the first 24 hours after application) typically due to blood clots or obstruction caused by the deformed plaque at the narrowed portion of the blood vessel. Late failure of such repairs can occur (usually about 3-6 months after application of therapy) due primarily to constriction of the passage through the blood vessel due to overgrowth of the smooth muscle portion of the blood vessel wall. The percentage of early failures is typically low while the percentage of late failures to relatively high (estimated at 40-70%).
More recently, attempts to overcome these problems have employed the use of stents that are placed in the blood vessels and left after the balloon angioplasty is performed. Examples of such techniques and equipment used to perform this repair are shown in the following patents:
______________________________________ U.S. Patent No. Inventor Issue Date ______________________________________ 3,868,956 Alfidi, et al. 03/04/75 4,776,337 Palmaz 10/11/88 4,922,905 Strecker 05/08/90 4,969,458 Wiktor 11/13/90 5,019,090 Pinchuk 05/28/91 ______________________________________
Experience has shown, however, that the stents have not been successful in overcoming the failures associated with balloon angioplasty. As a matter of fact, the stems have tended to fail more frequently than balloon angioplasty without the stents.
There have also been attempts to reduce blood clotting by using certain materials or circuits that generate an electronegative charge on the surface of artificial blood vessels used to surgically replace sections of the patient's vascular system or on the surface of receptacles to store blood. Examples of such techniques are illustrated in the following patents:
______________________________________ U.S. Patent No. Inventor Issue Date ______________________________________ 3,512,183 Sharp, et al. 05/19/70 3,723,754 Murayama, et al. 03/27/73 3,726,762 Puharich, et al. 04/10/73 ______________________________________
This technology has not been applied to nonsurgical balloon angioplasty in which the original blood vessel is not removed. As a matter of fact, prior art U.S. Pat. No. 3,512,183 suggests that this technology is not applicable to living tissue in the blood vessel.